1. Technical Field
This invention relates to electromagnetic solenoid assemblies and particularly to an electromagnetic solenoid having independently controllable forward and retract coils for use in actuating a rapper for removing slag from heat transfer tubes or walls of heat exchanger components.
2. Description
Trash burners and large scale boilers used by public utilities and industry are often fired by ash-producing fossil fuels. The internal surfaces of the heat exchanger often become fouled with ash encrustation during use. Such fouling adversely effects the heat transfer efficiency of the heat exchanger. Accordingly, it is necessary to provide a system for cleaning the heat exchanger surface.
One type of system presently in widespread use for de-slagging heat exchanger surfaces employs so-called sootblowers. These devices have a lance tube with a nozzle at its outer end which projects a fluid medium such as water, steam or air against the fouled surfaces. The thermal shock and mechanical impact caused by the blowing medium break away the slag encrustations from the heat exchanger surfaces.
Although sootblowers generally operate satisfactorily and are superior devices in many applications, they have certain limitations. Sootblowers consume a substantial amount of blowing medium which is a direct expense to the operator of the heat exchange facility. Additionally, sootblowers are unable to reach the areas of the heat exchanger which are inaccessible or beyond the effective range of the discharged blowing medium. Perhaps most significantly, however, is that sootblowers clean surfaces to bare metal, thus leaving them susceptible to high corrosion in highly corrosive and acidic environments.
Another system for removing encrustations from heat exchanger surfaces is through the use of mechanical rappers. Such rappers typically have an impacter which through some mechanical linkage strikes a surface within the heat exchanger in order to produce a mechanical vibration which causes the ash encrustation to disintegrate or loosen its adhesion to the heat exchanger surface. A principal advantage of mechanical rappers with respect to sootblowers is that mechanical rappers do not remove the protective oxide layer on the surfaces of the tubes, thereby enabling the oxide layer to help protect the surfaces of the tubes from corrosive environments. Mechanical rappers can be manually, pneumatically or electrically actuated.
One approach for providing an electrically actuated rapper is to employ a solenoid which is propelled forward against an impact target. Such a rapper could be designed to include a spring for retracting the impacter after the impacter has been mechanically or otherwise caused to impact or actuate its associated mechanical linkage during a rap sequence period. Such springs, however, provide drawbacks in that they typically wear out relatively quickly and also cause additional vibration in the mechanical impacter itself.
Another drawback in conventional mechanical rappers has been the inability to accurately control the force with which the impacter impacts the heat exchanger or mechanical linkage in contact with the heat exchanger. In certain applications, it would be desirable to have a mechanical rapper whose impacter element is controllable, to thereby provide control over the force with which the impacter element impacts its heat exchanger tubing or associated mechanical linkage.
It is therefore a principal object of the present invention to provide an electromagnetic hammer rapper which is operable to be propelled into impact or retracted positions without the aid of springs or other mechanical biasing means.
It is a further object of the present invention to provide an electromagnetic hammer rapper operable to retract its impact element in a relatively smooth, vibration-free fashion.
It is still a further object of the present invention to provide an electromagnetic hammer rapper having an impact element whose impact force may be controlled by an operator.